Video sequence editing, cutting strips
In the VSE you can cut a strip at the current frame by pressing K, which gives a "soft cut". You can also perform a "hard cut" at the current frame by using &#8679; ShiftK

The two strips resulting from a cut still know the video that they are from and frames that were "cut" from the strip can still be recovered.

The difference between a hard and soft cut is that with a soft cut you can drag the start of the clip to recover frames before the cut, while with a hard cut this will duplicate the frame at the cut to the adjusted start of the clip. This works the same for the end of the strip.

In both cases you can adjust the start and end frame by adjusting the strip input properties - press N to show the properties region.